1. Field
Exemplary embodiments of the present invention relate to a nonvolatile memory device and a method for fabricating the same, and more particularly, to a three-dimensional (3-D) structured nonvolatile memory device in which a plurality of memory cells are stacked in a vertical direction over a substrate and a method for fabricating the same.
2. Description of the Related Art
A nonvolatile memory device retains stored data although the power is not supplied. A variety of nonvolatile memory devices, such as flash memory, are being widely used.
As the improvement of the degree of integration of two-dimensional (2-D) structured nonvolatile memory devices with memory cells that are formed over a semiconductor substrate in the form of a single layer has reached the limit, there has been proposed a 3-D structured nonvolatile memory device in which a plurality of memory cells is formed along channel layers in a vertical direction from a semiconductor substrate. More particularly, the 3-D structured nonvolatile memory device is mainly divided into a structure having a straight-line type channel layer and a structure having a U-shaped channel layer.
In the structure having a U-shaped channel layer, a pipe connection transistor is used to couple memory cell strings. However, there is a concern in that electric resistance may increase, because the gate electrode of the pipe connection transistor (hereinafter referred to as a pipe connection gate electrode) is mainly made of polysilicon. In particular, an increase in the height of the pipe connection gate electrode to reduce the electric resistance of the pipe connection gate electrode may be limited and may become ineffective in a subsequent process.